Hi, In regards to your question about water & ice shield, I am a contractor in New England, where the winters are pretty rough. (probably not as tough as Winters in Canada. Anyways, "Ice & Water Shield" is much more than a self stick felt paper. It is a 1/16 - 3/32 " layer of what is technically known as Bichothane.(Spelling might not be 100%) Anyways, this material is an excellent way of preventing ICE DAMS. Ice dams are when the Melting ice turns to water and rolls down your roof & collects at the eves and then refreezes,which causes a dam to form which in turn causes more melting water to back up the roof under the shingles.Once it backs up about
10-12 " UNDER the shingles it may leak into the roof structure through the nail holes. The thing about Bichothane is that when a nail penetrates it, it is self-healing and seals around the nail,resulting in a water proof attachment. It is an inexpensive "insurance" against common leaks. If you really wanted a leakproof roof, you could put "water & ice " shield all the way up to the peak of the roof. Not too many people do this because the cost of the material alone is about $.40 a square foot. But it is common to put this membrane along the eves because that is where the water collects and refreezes in the winter.Also another common place to put water and ice shield is in the vallies on the roof. This is because water can collect in the winter and refreeze at these points also, and depending on how your roofer lays the shingles in the valley, more leaks tend to occur in sa valley that is cut in place rather than "WEAVED". (a good roofer will WEAVE his vallies)
All being said, the cost to you should only be about $1.50 - $2.00 U.S. per lineal foot of roof per side,and per lineal foot of run for the vallies.
I really can't see trying to save a couple of hundred dollars to skip on the assurance warer and ice gives you against the costly repairs that may happen such as rot in your walls, roof sheathing, ruined sheet-rock etc.
I hope this may give you some insight to the realities of using the water and ice sheild. (An excellent brand of water and ice shield is GRACE, it is the only one I personally use.)